The musical recently fell below 3 million viewers and a 1.0 rating in the key 18-to-49 demographic, matching its series low this week with a 0.9. It is among the lowest-rated series already renewed for the 2014-15 season, though the current batch of 22 episodes has been reduced to 20 as a result of a production hiatus at the start of the season. Fox might film the two cut episodes early to better promote what could be a supersized 24-episode sixth and final run.

Glee has trended down the past few seasons, but the slide during season five, its first since the July death of star CoryMonteith, has been more precipitous. The show jumps 54 percent to 6.5 million viewers and 63 percent in the demo to a 2.6 when factoring in DVR, but that's a far cry from season one's 11 million viewers and 4.9 rating. (Sans DVR, season five is averaging 4.2 million viewers and a 1.6.)

"Glee is still a great property to have on our air," says Fox COO JoeEarley, citing statistics that show it remains a top 10 comedy among teens and viewers with household incomes above $100,000. "There have been some scheduling challenges … but what we see is still an incredibly popular show with a lot of time-shifting."

With Fox moving to a year-round schedule, the network could experiment by airing Glee in unorthodox time slots. Adds co-creator Ian Brennan, "With DVR, in a lot of ways the night you air … doesn't matter."

Here's a look at Glee's ratings history:

Season averages (including live-plus-7 DVR):

Season 1: 4.9 million 18-49, 11 million total viewers
Season 2: 4.4 million 18-49, 10.9 million total viewers
Season 3: 3.8 million 18-49, 9 million total viewers
Season 4: 3.4 million 18-49, 8.4 million total viewers
Season 5*: 2.7 million 18-49, 6.8 million total viewers